[jfisher34]

i put a new carb kit in my 85 trx250 fourtrax. the reason was because it was running really rough when i rev'd it and it had been sitting for years. That seemed to take care of that problem. Now though, even though it idles really nice, if i give it just the slightest amount of throttle and hold it there, it will start to sputter and miss and sometimes shut off. Do i have the air/fuel screw too rich on fuel possibly?

thanks

 

[SamUK]

The key to setting fuel/air mixture is by looking at the colour of the spark plug. A general guideline for mixture is to start at 2 1/2 turns out and tweak it from there, however....

IF your carb kit is an aftermarket Chinese, eBay, Amazon etc item then it stands a very good chance of never running right.

Can you post a photo of your spark plug?

 

[jfisher34]

It is the original carb I believe. Spark plug is brand new and i have only run it for several minutes. not sure that will show anything however there is some black smoke coming out when i rev it. that is the other reason i think the fuel might be rich??

if the screw is on the back side of the carb (away from the gas tank), does that control the air and not the fuel? so "out" would let more air and "in" would restrict air?

 

[SamUK]

Okay, the OEM carb is the one to stick with for sure.
Is the enrichment valve stuck at all or is the seal perished? That could cause you issues. The mixture screw if I remember rightly is on the bottom of the carb just infront of the float bowl, it’s been a while since I rebuilt a 250 carb but I’m sure that’s it’s location.
IN will lean the mixture, OUT will richen the mixture. Do you know how many turns out you are already?

 

[jfisher34]

i took the entire carb apart, cleaned it in a simpe green solution in an ultrasonic cleaner and then put an entire new kit in it with gaskets. You are right that it sits in front of the bowl now that i'm remembering. so it does control the fuel mixture not the air mixture...correct?

i started with 2.75 turns out (that is what the old one was) and then adjusted it to the highest rpm. i cant remember where that ended up.

 

[SamUK]

Yes that’s it. So 2.75 out is probably to much, hence the black smoke your experiencing, usually you’d be between 2 1/4 to 2 1/2 turns out.
Highest rpm isn’t quite right, you’ll screw in until idle starts to lower, then out until idle starts to raise and then find the middle ground, that would be the correct procedure. Usually works out at 2 1/2 out though as I said

 

[retro]

i put a new carb kit in my 85 trx250 fourtrax.

If the carb kit you bought was any brand other than a genuine Shindy kit, you'll have to put all of your OEM parts back in it to fix it. Let us know how it goes if you can.

 

[jfisher34]

SamUK was right. after closer inspection, I ended up having the mixture screw set wrong. i put it back to 2.5 turns out and she is running much better. Thanks for the help.